Navigation systems are available that provide end users with various navigation-related functions and features. For example, some navigation systems are able to determine an optimum route to travel along a road network from an origin location to a destination location in a geographic region. Using input from the end user, and optionally from equipment that can determine the end user's location (such as a GPS system), the navigation system can examine various potential routes between the origin and destination locations to determine the optimum route.
The navigation system may then provide the end user with information about the optimum route in the form of guidance that identifies the driving maneuvers required to be taken by the end user to travel from the origin to the destination location. The guidance may take the form of visual and/or audio instructions that are provided along the way as the end user is traveling the route. Some navigation systems are able to show detailed maps on displays outlining the route, the types of maneuvers to be taken at various locations along the route, locations of certain types of features, and so on.
In order to provide these and other navigation-related functions and features, navigation systems use geographic data. The geographic data may be in the form of one or more geographic databases that include data representing physical features in the geographic region. Roads in the geographic region may be represented in the geographic database with one or more road segments. Each road segment is associated with two nodes; one node represents the point at one end of the road segment and the other node represents the point at the other end of the road segment. Alternatively, roads may be represented with curves, such as spline, Bezier, and clothoid curves.
The geographic database also includes information about the represented roads, such as one-way streets, position of the roads, speed limits along portions of roads, address ranges along the road portions, turn restrictions at intersections of roads, direction restrictions, such as one-way streets, and so on. Additionally, the geographic data may include points of interests, such as businesses, facilities, restaurants, hotels, airports, gas stations, stadiums, police stations, and so on.
Although navigation systems provide many important features, there continues to be room for new features and improvements. For example, some navigation systems calculate routes to minimize the vehicle's CO2 emissions. Such a route is sometimes referred to as a “green route.” There are many factors that determine a vehicle's fuel consumption as the vehicle travels along a particular route. These factors include speed of travel, traffic light and sign locations, weather, and road surface type, slope, and curvature.
To calculate a green route, the navigation system uses a route calculation algorithm, such as the A* search algorithm. Prior to calculating a route, a cost is assigned to the road segments or curves stored in the geographic database. For green routing, the cost is based on the road properties of the represented road and how these road properties impact fuel consumption. The route calculation algorithm evaluates different possible routes from an origin to a destination and identifies the route with the least cost.